Communication systems are widely used in computer and device networks to communicate information between computers and other electronic devices. Transceivers of a communication system send and receive data over a link (including one or more channels) of a communication network to communicate with other transceivers. A transceiver includes a transmitter for sending information across a link, and a receiver for receiving information from a link. The receiver detects transmitted data on the link and converts the data into a form usable by the system connected to the transceiver. For example, one widely-used network communication standard is Ethernet, including several different standards for different network bandwidths, including 10GBASE-T allowing 10 gigabit/second connections over unshielded or shielded twisted pair cables.
The IEEE 802.3an standard specifies 4 pairs of unshielded twisted copper as the communication channel in 10GBASE-T Ethernet systems. Each transceiver consists of 4 channels, each transmitting on one pair and also receiving on the same pair simultaneously. This scheme is similar to what is used in the older generation of Ethernet over copper. However, since the signal bandwidth in 10GBASE-T is much wider than the older generations, the standard recommends a better quality of cabling which offers lower insertion loss and lower crosstalk.
There are multiple sources of impairment and interference in a 10GBASE-T system which can cause significant performance degradation. These sources of impairment and interference can be broadly categorized as internal and external sources. The internal sources are caused by the link-partners themselves and imperfect channel characteristics. Examples of these sources are inter-symbol interference (ISI), echo and pair-to-pair cross-talk such as far-end crosstalk (FEXT) and near-end crosstalk (NEXT). Such noise sources are known to the link partners and thus can be cancelled effectively with cancellers and equalizers. These sources are very well characterized not only in the 10GBASE-T standard but also in the standards for older generations of Ethernet over copper. There are also well-known solutions to cancel, reject or mitigate the effects of these impairments in these standards. The signal source that causes these types of noise is known to the subject link or port experiencing the noise, and so this type of noise can be readily cancelled in that link.
Another type of impairment in 10GBASE-T systems is interference from sources external to a particular link. Examples of external interfering sources, referred to herein as alien interferers, include adjacent cross-talking Ethernet ports/links, where the noise source is from a different port or cable that is adjacent to the subject link (port) and thus the source of the interference is unknown to the subject link, and is a greater challenge to reduce than noise originating from a known source such as ISI, echo, FEXT, and NEXT. Alien interference also can include RF interference (RFI), which is produced from external unknown sources including RF interferers such as mobile phones, walkie-talkies, etc. These interferers are particularly harmful in 10GBASE-T technology because of its wide signaling bandwidth. The effects of these interference sources and methods to mitigate those effects are not widely understood, and are not well addressed or supported in existing standards. For example, the 10GBASE-T standard allows for the reduction in alien crosstalk only through a power backoff mechanism, in which signal power is reduced to reduce crosstalk if the link cable length is short enough to permit such a power reduction. However, this mechanism is not adaptable to any particular alien interference, and thus, for example, does nothing to address alien crosstalk that exists for greater signal power over long cable lengths or at backed-off power levels, nor alien interference from other sources. Consequently, alien interference sources can present difficulties for the desired performance of high bandwidth communication systems.
Accordingly, what is needed are systems and methods that reduce or cancel alien interference in channels of communication systems, providing more robust communication in such systems.